1. Technical Field
The present invention relates to the process of assembling and testing a product, and, more specifically, a highly flexible process capable of handling both large jobs and small jobs efficiently by minimizing any impact from job change-over and optimizing cycle times.
2. Background Art
A manufacturing process for electronic equipment such as computers includes assembly, inspection, and testing. Assembly involves installing the various components including cables, labels, screws, etc. The assembly operators must be able to build many different products. The smaller the job size, the more frequently the operators will have to change to a new product. Each unit is inspected and tested to ensure proper cable routing and component installation.
In computer manufacturing, testing typically includes a configuration test, a run-in test, a software pre-load onto the hardfile, a verification test, and a high potential (hi-pot) test. These tests are either initiated from a floppy disk or through a Local Area Network (LAN) with minimal code on the diskette. A LAN is the most efficient way to test the product and pre-load the hardfile. This requires the installation of a LAN card in the assembly process. For customers that did not request a LAN card, a temporary slave card is installed which must be removed prior to the verification test. A hi-pot test is required to verify that the unit is safe and to get UL approval.
If a unit fails one or more of the tests, it must be debugged. This includes both component failures and workmanship-induced failures. Replacement parts must be made available to the debug operator. Once the failure is verified, the faulty part is tagged and replaced. A floor control system is used to track the unit through the process. The system ensures that all steps are completed and all tests are passed.
Manufacturing setup time includes parts presentation to assembly and debug, ensuring the correct test code and preload are available, and familiarizing the operators with the assembly process for the new product. In a manufacturing cell environment where operations have been streamlined, it is critical that setup times are reduced. It is also critical that cycle times are optimized to minimize the time from when an order is placed until it is shipped.
There are many ways to lay out a manufacturing line to maximize efficiency depending on the business strategy. If the strategy is based on large orders of a specific product (i.e. build to plan, build to order for a dealer, etc.), large lines with material handling solutions are often implemented. If the strategy is oriented towards small orders (i.e. build to order for specific customers), workcells with minimum material handling are typically used.
Conventional methods typically work well for one strategy or the other, but not both. A large manufacturing line usually has separate areas for assembly, inspection, configuration, run-in, pre-load, card removal, verification, hi-pot, and packaging, including queues between each area. Large lines work best when they are fully staffed; otherwise, significant balancing between operations is required. One downfall of this approach is the intrinsic separation between operations (an assembler has little awareness of how a workmanship error impacts configuration). If the inspection area finds an error, there may already be numerous units in the queue with the same error. These circumstances reduce the ownership felt by the operators. In addition to this risk, WIP inventory is higher due to the queues between operations.
Testing products on a large line is typically done to optimize workload. Gravity conveyors, carts, or other equipment is frequently used for this purpose. Due to the sensitivity of hardfiles, a lane or cart has to be fully loaded before the units are powered on for testing. The sensitivity is due to the risk of a unit being brought into test hitting one that is already powered on, thereby causing possible hardfile damage. Consequently, this risk increases the cycle time for those units that arrive early to a lane. If a unit in the middle of the batch fails, the whole batch is held up during repair. In addition, it is more efficient for the operator when all the units in a batch are the same. Otherwise differences in test times and processes reduce efficiency as all of the units must wait for the longest requirement to complete. For large batches of the same product, these impacts are minimized.
Cells are usually designed for specific product families using Group Technology theories. The "textbook" cell is often used for machining operations, not assembly and test. The traditional Group Technology workcell recommends dedicating cells to specific products (e.g. different cells would be used for each product type with different parts or processes). Because of varying product demand, dedicating cells to specific product types restricts the ability of process designers to optimize capacity and staffing. For example, some manufacturers have implemented cellular-based concepts that divide operations. These designs have assembly cells and separate testing and burn-in areas. Thus, although the assembly process is improved, WIP is increased due to queues, loss of ownership resulting from separation of operations, and staffing imbalances between areas.
Unfortunately, it is impractical to install both manufacturing cells and large lines to solve these problems. Such a facility would incur even higher costs and decreased efficiency since fixed support structures would be required in both areas. Physically separate lines would require management to round up for staffing needs in both places, thereby reducing their ability to optimize staffing.
What is needed is a manufacturing line with ultimate flexibility that is able to assemble and test any product on any cell efficiently regardless of job size.